#include <bits/stdc++.h>

using namespace std;
const int maxn=10010;
int main_1041()
{
    int N,num;
    scanf("%d",&N);
    int numbets[N]={0},cnt[maxn]={0};
    for (int i=0;i<N ; ++i)
    {
        scanf("%d",&num);
        numbets[i]=num;
        ++cnt[num];
    }
    bool isRepeat=true;
    for (int j=0;j<N ;++j )
    {
        if (cnt[numbets[j]]==1)
        {
            isRepeat=false;
            printf("%d",numbets[j]);
            break;
        }
    }
    if (isRepeat)
    {
        printf("None");
    }
	return 0;
}
